1. Field of the Invention
The present invention generally relates to optical communication systems. More particularly, the present invention relates to actuators utilized in optical communication systems such as optical cross connects (xe2x80x9cOXCsxe2x80x9d) for use in fiber optics communications.
2. Description of the Related Art
In the field of optical communications, the industry is constantly striving to improve the quality of optically communicated information and improve the efficiency with which this information is communicated. While there are methods and systems for steering beams of light, the actuating and alignment mechanisms utilized within these systems remain inefficient. Further, many of the current beam steering systems are not suitable for optical communications applications, such as optical cross connects (OXCs). For example, U.S. Pat. No. 5,696,421 to Zumeris et al., incorporated herein by reference, describes a spherical element driven in two degrees of rotation by four indirectly connected piezo actuators and U.S. Pat. No. 4,727,728 (the ""728 patent) to Staufenberg, Jr. et al., incorporated herein by reference, describes a spherical element movable in two degrees of rotation by three piezoelectric transducers. The ""728 patent also discloses the use of a mirror attached to the spherical element to direct a laser beam. Both of the above mentioned patents used a vibratory driver comprised of a piezoelectric element that is made to move (or to move another part) by the vibrations generated in the piezoelectric element.
Conventional vibratory drivers are described in U.S. Pat. No. 4,019,073 to Vishnevsky et al., U.S. Pat. No. 5,453,653 to Zumeris and U.S. Pat. No. 5,140,214 to Kimura et al., each of which is incorporated herein by reference in its entirety. Actuation is effected by a piezo element when the piezo element is made to move in an oscillatory motion. The oscillations are made to create stronger friction in one direction. For example, in one part of the oscillation the piezo element is moving slowly, dragging a movable part, while in the reverse the piezo element moves fast, causing a slip of the friction surface due to the inertia of the moving part. This mode of drive is referred to herein as point vibration actuating.
Another conventional way of creating motion is by using standing or moving vibration waves that travel parallel to the contact area between a moving part and a stationary part of an actuating system. The moving part and the stationary part touch each other in a series of points along a pre-established contact area. In a conventional system, a piezoelectric transducer creates the vibration waves and creates the motion. The actuation effectively results from a shortening or elongating of the distance between the points where the stationary part and the moving part touch each other. Examples of systems utilizing standing or moving vibration waves are shown in U.S. Pat. No. 4,882,500 to Iijima disclosing linear and rotational actuators, while U.S. Pat. No. 6,072,266 to Tomikawa describes two degrees of perpendicular motion using such driving mechanism. These patents are incorporated herein by reference in their respective entireties. This mode of actuating is referred to herein as surface vibration actuating.
Yet another conventional method of creating relative motion is by creating ultrasonic waves in a piezoelectric material. These are traveling waves. The crests of the waves are in contact with the moving part and create a driving force. Examples of this type of motion creation are described in U.S. Pat. No. 5,311,094 to Imasaka et al., U.S. Pat. No. 4,945,275 to Honda and U.S. Pat. No. 4,739,212 to Imasaka et al., each of which is incorporated herein by reference in its entirety. The frequency usually used to drive these actuators is in the ultrasonic range, and these type of drivers are referred to herein as ultrasonic actuators.
Piezoelectric materials posses non-diagonal elements of the tensor of elasticity that are non-zero. This phenomenon causes a piezoelectric material to change dimensions upon application of electric field to the piezoelectric material. A single-crystal piezoelectric material has an electric polarization vector built-in due to the crystalline structure. A ceramic piezoelectric material is poled with high voltage to arrange the small crystalline domains in one direction prior to use as an actuating material. FIG. 1A shows a piezoelectric material coated on two sides with conducting layers. In FIG. 1A, only one layer is visible while the second layer is coated on the opposing side of the piezoelectric material. Electrical wires are connected to the conducting layers, making these conductive layers equivalent to first and second electrodes.
Referring to FIG. 1B, a side view of the structure illustrated in FIG. 1A, the first and second electrodes are visible. The electric polarization vector is along the Z dimension. When positive or negative voltage is applied between the first and second electrodes, as in FIGS. 1C and 1D, an electric field is imposed between the first and second electrodes, along the Z dimension. As shown in FIG. 1C, the electric field causes the piezoelectric material to expand in the X and Y dimensions, and contract in the Z dimension. As shown in FIG. 1D, a reversed electric field causes the piezoelectric material to contract in the X and Y dimensions and expand in the Z dimension. In this embodiment, the electrodes are thin so as to comply with the dimension changes of the piezoelectric material.
Referring to FIG. 2, a mechanism using the piezoelectric phenomenon for linear motion is illustrated, as shown in U.S. Pat. No. 3,902,084 to William May, Jr., incorporated herein by reference in its entirety. A movable shuttle is a cylindrical rod. The shuttle is rigid and does not change dimensions. The shuttle is inserted into a hollow comprised of clamps that can be made to contract with proper voltage applied, gripping on the shuttle. When not clamped, the clamps slide freely on the shuttle. There is also a tube, having clamps attached at either end, that may elongate or contract along the cylindrical axis, with application of the proper voltage. By applying voltages in a specified order through electrodes and wires, the shuttle is made to travel right or left. Each step is very small, on the order of a micrometer. The motion resolution is a small fraction of one step and is in the nanometer range. In each step, one clamp is made to contract, the tube is extended (or contracted) and then the other clamp is contracted. Then the first clamp is released, and the tube contracts (or extends). The result is a movement of the shuttle relative to the tube/clamps cylinder. When several steps are taken, the motion is similar to the movement of an inch worm, therefore the trade name of the product. The cost of this product is quite high, due to the fine and accurate surface finish required on the surfaces in contact. The shuttle and grippers are usually lapped and polished ceramic parts. The reason is that the grippers can contract in diameter a very small amount, a few micrometers at most.
U.S. Pat. No. 5,563,465 issued to Nakahara et al. and incorporated herein by reference in its entirety, describes a mechanism where piezoelectric element can, when elongated, contact a shuttle at an angle and push it. Several elements are aligned in different directions to enable movement in two directions, along one degree of freedom.
U.S. Pat. No. 5,396,142 issued to Koblanski and incorporated herein by reference in its entirety, shows a piezoelectric mechanism that creates waves in a coupling member that pushes a shuttle.
U.S. Pat. No. 5,994,820 issued to Kleindiek and incorporated herein by reference in its entirety, describes tube shaped actuator with a slider consisting in part of elastic material that controls the friction forces.
U.S. Pat. No. 4,422,002 issued to Binnig et al. and incorporated herein by reference in its entirety, shows a moving mechanism with two degrees of freedom. In FIG. 3, as it appears in the Binnig et al. patent, the shuttle is a flat part contacting three legs. Application of electrostatic voltage between the legs and the shuttle creates clamping forces. The difficulty with such design is that electrostatic forces are small and quite high voltages will be needed. The actuator systems described above are affected by outside environmental forces such as shock and vibrations. As such, it is important to hold the actuator shuttle in place against these forces; and, voltage should be applied at all times to hold the clamps locked. The electrostatic clamping described by Binnig et al. will not be sufficient to hold the shuttle in place even if it is applied at all times.
The embodiments of the invention described herein set forth piezoelectric motors, actuator configurations, optical cross connect (xe2x80x9cOXCxe2x80x9d) configurations and alignment/servo systems, as well, as the methods for using the same, either alone or in various combinations.
An embodiment of the present invention describes an actuator comprising a piezoelectric element having at least one electrode on two opposing surfaces thereof, at least two magnetic elements contacting the piezoelectric element; and a shuttle, wherein movement of at least one of the piezoelectric element, the at least two magnetic elements, and the shuttle is electromagnetically controllable by the piezoelectric element and the at least two magnetic elements.
Another embodiment of the present invention describes a beam steering unit comprising a first and a second piezoelectric element, a frame, a base wherein the frame is rotatably attached to the base, and at least one movable optical element, wherein the at least one movable optical element is rotatably attached to the frame, and further wherein the first piezoelectric element operates to move the frame in a first degree of freedom and the second piezoelectric element operates to move the at least one movable optical element in a second degree of freedom, such that a beam impinging upon the movable optical element is steerable in two degrees of freedom.
A further embodiment of the present invention describes an optical cross connect comprising a first and a second modular unit, wherein each of the first and second modular units includes a predetermined number of beam steering units and a predetermined number of beam generating units, such that there are an equal number of beam steering units and beam generating units within each of the first and second modular units, and at least one input fiber for supplying a transmission signal to at least one of the predetermined number of beam generating units of the first modular unit and at least one output fiber for receiving the transmission signal from at least one of the predetermined number of beam generating units of the second modular unit, wherein each of the predetermined number of beam steering units includes at least two piezoelectric elements and at least one movable optical element for steering the transmission signal in two degrees of freedom.
A still further embodiment of the present invention describes a method for steering a data signal through an optical system comprising receiving a data signal from an input fiber, generating a data beam from the data signal via a first beam generating unit, determining an output fiber to which the beam is to be directed, adjusting the direction of the beam via at least one beam steering unit, transforming the data beam back into the data signal via a second beam generating unit, and receiving the data signal into an output fiber, wherein the at least one beam steering unit includes at least two piezoelectric elements and at least one movable optical element for steering the data beam in two degrees of freedom.
For each of the systems and methods described herein, when light is made to travel from an input unit to an output unit via, for example, beam generating units and beam steering units, light can also travel in the reverse direction, from the output unit to the input unit. There is a full symmetry between the input and output units. However, the terms xe2x80x9cinputxe2x80x9d and xe2x80x9coutputxe2x80x9d are used throughout the specification for ease of explanation, without limit of the applicability of the described system for light transmission in the reverse direction or for light transmission in both directions simultaneously.